Objectives: (1) To determine the effect of proportional, integral and derivative information carried by the alveolar PCO2(t) and Po2(t) signals on the rate and depth of breathing. (2) to study normal information processing in a biological control system without disrupting the system. (3) To use "dialectical modeling" (i.e., model, experiment, remodel, etc. ...) to informationally dissect the respiratory control loops. This study will use an awake, unidirectionally-ventilated chicken preparation to (1) determine the parameters of the ring oscillator which acts as the pacemaker for avian respiration, (2) elucidate how peripheral CO2 receptors affect tidal volume, (3) analyze the dynamics of O2 control and (4) study the interrelationships of CO2 and O2 control.